I have heard that skiers and snowboarders can do a lot of damage to an ecosystem. I am interested in the following backcountry wintersport activities and would like to do them responsibly.

cross-country skiing

snowshoeing

ascending with snowshoes and descending by snowboard

I have the following questions:

At what snow-cover depth are little saplings, bushes and mountain-tundra vegetation protected from those activities?

Is it best to go to wilderness areas that are already being impacted by backcountry winter sports, or does this increase the damage done to those habitats, making it a better choice to go to places that have not been impacted?

What do I need to know about minimizing my impact on the local fauna?

Are there types of ecosystems that I should not enter at all for these activities, since any kind of disturbance could cause long-lasting damage?

That should depend a lot on the elevation. Ski on a glacier that has snowcover 10–11 months per year and it should be fine...
–
gerritFeb 1 '13 at 21:05

1

It depends a lot on the snow conditions too. Alpine tundra is the most fragile of the vegetations you mention, but it is also usually covered with the hardest snow. Just 3 inches of hard snow should protect it well enough. Look at your tracks. Are you hitting ground, or is there always a layer of snow under your footprints?
–
Olin LathropFeb 1 '13 at 22:37

You do mention the tops of saplings sticking up. Avoid them. If when you pass on your board you see broken saplings in your wake, the snow is not deep enough. Use common sense.

As for local fauna - they're all pretty used to hiding in holes anyway, and your passing by on skis likely won't disturb them. (A major exception is elk and deer calving grounds, which are often identified on US public lands maps, and are usually closed to snowmobiles and sometimes skiers.)

The impacts you DO need to be concerned about are waste, trash, and etc. that easily get buried beneath snow where they seemingly "disappear." Pack it in, pack it out.

Of course, the biggest impact from non-motorized winter recreation is the motorized facilities of ski resorts which consume vast amounts of electricity to haul people up on lifts, diesel fuel to run snow cats that make those perfectly groomed trails, and development impacts that can encroach into wild lands.

There is one often forgotten thing in skiing that can be harmful. The waxes. The racing ones contain a lot of fluorocarbons that can stay in the environment for ages. The pure racing fluorocarbons (mostly powders) are dangerous even to people applying them and special masks should be worn (see). Consider using just pure hydrocarbon waxes or other waxes marked as environment friendly when not taking part in competitions.